1 / 17

Microbial growth: chapter 6

Microbial growth: chapter 6. Population growth. Increase in cell number or cell mass of population Growth rate change in cell number or mass/time Generation the interval of two cells from one Generation time (doubling time) time for cell mass or # to double Varies greatly

thora
Download Presentation

Microbial growth: chapter 6

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Microbial growth: chapter 6

  2. Population growth • Increase in cell number or cell mass of population • Growth rate • change in cell number or mass/time • Generation • the interval of two cells from one • Generation time (doubling time) • time for cell mass or # to double • Varies greatly • Type of organism • Temperature • Nutrients • Other conditions • Norm= 1-3 hours • Exponential growth (Log phase growth) • When population doubles/ unit of time

  3. Bacteria grow exponentially • Most bacteria divide in a short amount of time and produce a large amount of bacteria – easier to represent these large numbers by logarithmic scales

  4. The number of cells produced after X-generations is better expressed logarithmically

  5. Generation time=the time it takes a microbial population to double in number • G = t/n • t = time of exponential growth • n = # of generations between original and final

  6. Mathematics of exponential growth • Nt = N0 X 2n • No = # of cells in population initially • Nt = # of cells in population at time t • n = number of generations that have occurred • log (Nt = NO X 2n) • log Nt = log NO + nlog 2 • log Nt- log NO= n log 2 • (log Nt- log NO)/ log2 = n • (log Nt- log NO)/0.301 • 3.3 (log Nt- log NO)

  7. Problemsdetermine the number of cells in a population at time t • 1. If you start with 1 cell how many do you have after 4 generations? • Nt = N0 X 2n • 16 = 1 x 24 • 2. If you start with 100 cells, how many do you have after 4 generations? • Nt = N0 X 2n • 1600 = 100 x 24

  8. Problem • 4. E. coli has a generation time of 20 minutes. If you start with 1 E. coli cell how many do you have after 2 hours? • Nt = N0 X 2n • 64 = 1 x 26 • If it is 2 hours, then 6 generations • 120 minutes/20 minutes = 6

  9. Problems: determine number of generations • 5. Example • If No = 1 X 104, Nt = 6.5 X 107, t =240 min. minutes, then what is the number of generations? • (log Nt- log NO)/ log2 = n • (Log (6.5 X 107 ) – log (1 X 104 ))/log 2 • Use your calculator to figure this out

  10. Problems: determine generation time • If No = 1 X 104, Nt = 6.5 X 107, t =240 min. minutes, then what is the generation time? • Use the formula, g = t/n • = g = 240 minutes/n (this you get from the last question)

  11. Plotting growth versus time: The smaller the generation time, the faster the growth. The faster the growth, the greater the slope in the line. G=6 hours; slope 0.05 G=2 hours; slope 0.15

  12. The growth calculations pertain to EXPONENTIAL PHASE ONLY! • Bacteria have other phases of growth also

  13. 1. Lag phase 2. Exponential phase – log phase 3. Stationary phase 4. Death phase Bacterial population growth undergoes 4 phases

  14. Lag phase • No increase in cell number • Synthesize macromolecules needed for protein synthesis and enzymes required for cell division • The length of the lag phase depends on: • Conditions of bacteria before transfer into growth medium • The content of the growth medium

  15. Log (exponential) phase • Cells are dividing at maximal rate • Cells are most susceptible to the action of antibiotics and other deleterious agents

  16. Stationary phase • Occurs when the number of viable cells stops increasing • Due to nutrients being used up and/or toxic products accumulating from cell’s metabolism

  17. Death phase • Exponential decrease in the number of viable cells • Dead cells are cells that can no longer multiply

More Related